Well, there are several places. First, AO3 is a great option. It has a large community of writers and a great tagging system, which makes it easier to search for 'saix oc fanfic'. Another place could be Tumblr. Some bloggers share fanfics there, and you might be lucky to find some good ones about Saix and OCs. Also, some dedicated fan communities or forums related to the source material of Saix might also have links or even host their own fanfics.
Finding good 'saix oc fanfic' can be a bit of a hunt. As mentioned before, Archive of Our Own is a top choice. The site has a very inclusive and diverse collection of fanfics. You can search by the character name 'Saix' and also look for tags related to original characters. FanFiction.net is also worth checking. It has been around for a long time and has a huge amount of content. Additionally, you could join relevant fan groups on social media platforms like Facebook or Reddit. Members often share and recommend fanfics, which could lead you to some excellent 'saix oc fanfic'.
Chapter 432, "Return to the Homeland!", is the clearest early answer because it pushes Jiang Mingyu into a new phase or setting. A useful checkpoint is the way the scene starts with Jiang Li had also received the updated rankings.
Chapter 410, "There's Something Wrong with This Lottery Box!", is the clearest early answer because it turns Sister Li's situation into a concrete plot event. Early on, Nina's voice had barely fallen when Pan Xing turned his gaze to Jiang....
Chapter 304, "Shh, Let's Not Disturb Big Sister", is the clearest early answer because it turns Big Sister's situation into a concrete plot event.
Chapter 182, "Director Sun Still Knows How to Stir Things Up", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event.
Chapter 448, "Has Jiang Li Gone Crazy?!", is the clearest early answer because it turns Notification's situation into a concrete plot event. It opens with Yu Li still wanted to persuade her, "Why not keep everything? and closes on Having her on his team was like having dead weight..
Chapter 138, "From now on, let's get to know each other again", is the clearest early answer because it turns Director Sun's situation into a concrete plot event. It opens with Is there such a good deal? and closes on Could it be that the poison also had a side effect of making a person....
Chapter 311, "Signed Jiang Yan", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 251, "It seems that going on a transformation show is really useful!", is the clearest early answer because it turns Fang Wenzhe's situation into a concrete plot event. It opens with If Du Qinglian was somewhat angry just a moment ago, now she was...
Chapter 199, "You Found Out Long Ago?", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. It opens with Damn, the production team is actually being so generous this time,...
Chapter 474, "Handcrafted Wooden Bed", is the clearest early answer because it turns Brother Pig's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Although everyone besides Jiang Li and Shang Shuyue was red-faced and...